Hard-Working Wasps Help Protect Apple
Crops

American apple growers in the Northeast can thank a European
import for helping them battle the tarnished plant bug, one of the fiercest
crop pests in North America. Agricultural
Research Service entomologist William H. Day, with the agency's
Beneficial Insects Introduction Research
Laboratory in Newark, Del., began releasing the parasitic wasp,
Peristenus digoneutis, as a biological control for the pest in the late
1970s and early 1980s.

The tarnished plant bug, Lygus lineolaris, is a pest of
fruits, vegetables, cotton, crops grown for seed and tree seedlings. It is
especially damaging to apples, strawberries and other fruits. Adult tarnished
plant bugs puncture the immature fruit to feed on its juices. As the fruit
grows, it becomes deformed at the bug's feeding sites. Many apples end up so
blemished or misshapen that they can't be sold, or can only be sold at a low
price--for cider making, for example.

Tarnished plant bugs often live in alfalfa fields, where they
feed and multiply even though they don't attack alfalfa itself. Then, when the
alfalfa is cut for hay, large numbers of them fly away and live on other
crops.

To counter the tarnish plant bugs in alfalfa, Day established
P. digoneutis in northern New Jersey alfalfa fields in 1984. Since then,
Day has been monitoring three tarnished plant bug-infested alfalfa fields in
northwestern New Jersey. During the past decade, Day has found that the
beneficial wasps reduced the plant bugs' numbers by 65 percent in these fields.
The parasitic wasp has spread from New Jersey into seven other northeastern
states, and into Canada. After the wasp arrived in New Hampshire, tarnish plant
bug damage to apples in that state dropped by 63 percent.

The tiny P. digoneutis wasp is harmless to humans, but
its females sting young plant bug nymphs and lay tiny eggs in them. About 10
days after the wasp eggs hatch into larvae, the nymphs die. Recent research has
shown that half the tarnished plant bugs in strawberries are killed by the
parasite, and additional research is under way to learn if fruit damage is
reduced.

More information about this research is in the May issue of
Agricultural Research magazine.